\[
\begin{align}
\frac{\Delta Y}{Y} & = k-c \times \Delta u \\ \\
Y & \textrm{ is actual output.} \\
c & \textrm{ is the factor relating changes in unemployment to changes in output.}\\
\Delta Y & \textrm{ is the change in actual output from one year to the next.}\\
\Delta u & \textrm{ is the change in actual unemployment from one year to the next.}\\
k & \textrm{ is the average annual growth rate of full-employment output.}
\end{align}
\]